[now primarily historical] Timesharing is the technique of scheduling
a computer's time so that they are shared across multiple tasks and
multiple users, with each user having the illusion that his or her
computation is going on continuously. John McCarthy, the inventor of
LISP, first imagined
this technique in the late 1950s. The first timesharing operating
systems, BBN's "Little Hospital" and CTSS, were
deplayed in 1962-63. The early hacker culture of the 1960s and 1970s grew
up around the first generation of relatively cheap timesharing computers,
notably the DEC 10, 11, and VAX lines. But these
were only cheap in a relative sense; though quite a bit less powerful than
today's personal computers, they had to be shared by dozens or even
hundreds of people each. The early hacker comunities nucleated around
places where it was relatively easy to get access to a timesharing
account.

Nowadays, communications bandwidth is usually the most important
constraint on what you can do with your computer. Not so back then;
timesharing machines were often loaded to capacity, and it was not uncommon
for everyone's work to grind to a halt while the machine scheduler
thrashed, trying to figure out what to do next. Early hacker slang
was replete with terms like cycle
crunch and cycle drought
for describing the consequences of too few instructions-per-second spread
among too many users. As GLS has noted, this sort of problem influenced
the tendency of many hackers to work odd schedules.

One reason this is worth noting here is to make the point that the
earliest hacker communities were physical, not distributed via networks;
they consisted of hackers who shared a machine and therefore had to deal
with many of the same problems with respect to it. A system crash could
idle dozens of eager programmers, all sitting in the same terminal room and
with little to do but talk with each other until normal operation
resumed.

Timesharing moved from being the luxury of a few large universities
runing semi-experimental operating systems to being more generally
available about 1975-76. Hackers in search of more cycles and more control
over their programming environment began to migrate off timesharing
machines and onto what are now called workstations around 1983. It took another ten
years, the development of powerful 32-bit personal micros, the
Great Internet Explosion before the migration was
complete. It is no coincidence that the last stages of this migration
coincided with the development of the first open-source operating
systems.